Low free formaldehyde melamine-formaldehyde detackifier and method of using

ABSTRACT

A melamine-formaldehyde detackifer having a less than 0.15% free formaldehyde which comprises a melamine-formaldehyde polymer detackifier to which has been added a formaldehyde scavenging agent selected from an effective amount of urea, acetylacetone, and a combination of urea with an enhancer selected from glyoxal and acetylacetone. The use of the low free formaldehyde detackifier is also described.

BACKGROUND OF THE INVENTION

Automobile parts, bicycles, toys, appliances and other industrial and consumer articles are conventionally spray painted in areas called spray booths wherein water curtains are employed to wash the air and to remove over-sprayed paint, lacquer or enamel solids. The wash water is then treated to remove paint solids, and the treated water is recirculated.

A water curtain is typically created by pumping water into a trough above the overspray area. The overflow from the trough is then controlled so that a uniform sheet of water falls along the length of the trough and down the booth's wall. Spray nozzles are also commonly used. Droplets of oversprayed paint, emitted by a spray gun, contact and are captured by the water curtain.

A major problem associated with spraying operations concerns the tacky or adhesive nature of the over-sprayed coating materials. Solids tend to agglomerate and accumulate on the walls, ceiling and floor of spray areas and to clog water spray equipment, recirculating pumps and the like. Thus, the overspray, or paint mist, captured in the water system of a spray booth must be detackified, or "killed", before it adheres to the walls, piping, etc. of the spray booth. Paint that sticks to spray booth surfaces usually cannot be easily removed from the equipment and tends to build up overtime, which hampers spray booth efficacy.

One solution, which has been found to have practical application to the overspray problem, involves the use of chemicals which, when added to spray booth water, detackify paint solids. A wide variety of chemical formulations have been proposed for this purpose, and have been described in coassigned U.S. Patent Application Ser. No. 185,720 C-1453IA dated Apr. 25, 1988 of Faust et al, the pertinent portions of which are incorporated by reference. The above enumerated Faust et al application relates to the use of melamine-aldehyde-type polymers, more specifically melamine-formaldehyde polymers, to kill over-sprayed paint. The polymer is used preferably in combination with at least one polymeric coagulant.

DETAILED DESCRIPTION OF THE INVENTION

The Faust et al formulation for example has the disadvantage that it contains excessive free formaldehyde. Since formaldehyde is a potential carcinogenic material its level should be reduced to less than about 0.15%, and preferably to less than 0.1%. A search of pertinent U.S. patent literature produced the following references: Patent No. 2,345,543 of Wohnsiedler et al, which describes cationic melamine-formaldehyde resin solutions; No. 3,723,058 of Reinhard et al, which describes removal of free formaldehyde from solutions of methylolated carbamate finishing agents and textiles treated therewith; No. 3,957,431 of Pal et al, which describes a process for easy care finishing cellulosics having low formaldehyde release; No. 4,120,840 of Hurlock et al, which describes the use of phosphorous acid to stabilize quaternized polyacrylamide and No. 4,127,382 of Perry, which describes a process for the reduction of free formaldehyde in textile fabrics. The latter patent uses a formaldehyde scavenger, which comprises a heterocyclic compound free of carbonyl groups and containing a NH group. Patent No. 4,612,556 of Moira, to a self-contained pressure sensitive copying material, describes the removal of free formaldehyde from a formaldehyde containing suspension of microcapsules by the addition of a compound having a beta dicarbonyl group or a cyclic ketone. Patent No. 4,686,047 of Arots describes a process for the detackification of paint spray operations.

None of the above art describes a melamineformaldehyde detackifier having less than 0.15% free formaldehyde using a formaldehyde scavenging agent selected from the group consisting of urea, acetylacetone, a combination of urea with an enhancer of glyoxal or acetylacetone. Although the inventor has ascertained that the above enumerated compounds provide the desired results, other materials have been tested and found wanting. These materials include, inter alia, phthalimide, dihydroxyacetone, hydrazine, melamine, phosphorous acid, ethylene glycol, baker's yeast, Candida boidini yeast cake, Pseudomonas putida cake, and cyanamid. Only urea, acetylacetone, mixtures thereof and mixtures of urea with glyoxal provide satisfactory results.

As can be seen from the tests, urea and acetylacetone can reduce the level of free formaldehyde down to below 0.15%. The use of glyoxal, however, does not so do. In some cases the urea resulted in the formation of a precipitate. This precipitate is believed to be primarily melamine formaldehyde with some urea formaldehyde. The addition of acetylacetone to urea at levels, where neither alone scavanged enough formaldehyde, greatly prevents precipitate formation and thus results in an effect greater than that of either product alone. This combination, however, is relatively touchy in that a precipitate may form. The use, however, of urea and glyoxal is relatively stable and yields clear solutions without precipitation or cloudiness.

The following examples demostrate the instant invention in greater detail. They are not intended to limit the scope of the invention in any way.

EXAMPLES 1-8

In these examples, one starts with a fine colloidal suspension of melamine-formaldehyde polymer such as Calgon Corporation's CA-289, which has a molecular weight of about 2,200, a pH of about 1.6 to about 2.1 and contains about 8% active melamine-formaldehyde as is further defined in the aforementioned Faust et al Application Ser. No. 185,720. To a 50 g aliquot of the resin suspension one adds the amount of scavenger specified in Table I below while stirring at room temperature. The starting urea-formaldehyde suspension had a free formaldehyde content of greater than 0.3% formaldehyde. The times at which the formaldehyde content of the treated material was evaluated are also set forth in the table. The effectiveness of the detackifier was evaluated as follows: For each product 200 mls of cold tap water was added to an open mouth one pint glass jar equipped with a magnetic stir bar. While stirring the jar at high speed, a carbonate ion source was added so as to provide an alkalinity of 1000 ppm (calcium carbonate basis), 0.5 ml of test product was then added to the jar. As stirring continued, 6 drops of a commmercially available white, paint as defined in Table I, were added to the jar. After 30 seconds, 2.0 ml of Calgon polymer 9230 (high molecular weight (5-6,000,000) copolymer of acrylamide and dimethyldiallyl ammonium chloride) was added to the jar. After 30 more seconds, the samples were evaluated. The results are given in Table I.

                                      TABLE I                                      __________________________________________________________________________     % H.sub.2 CO                                                                   Ex.                                                                            No.                                                                            Remarks                                                                             Treatment     Time   Found                                                                               Scavenged                                       __________________________________________________________________________     1    3.0 g acetylacetone; orange;                                                                 3  hrs.                                                                               0.16  47*                                                 sl. haze; phenol type odor                                                                   1  day 0.073                                                                               79                                                                 2  days                                                                               0.059                                                                               83                                              2    1.0 g urea; turns from                                                                       3  hrs.                                                                               0.063                                                                                79*                                                 opalescent to cloudy                                                                         24 hrs.                                                                               0.027                                                                               92                                                                 48 hrs.                                                                               0.030                                                                               91                                              3    1.0 g urea; hvy cloud                                                                        24 hrs.                                                                               0.036                                                                                89*                                            4    2 g urea; opalescent @                                                                       24 hrs.                                                                               0.035                                                                                90*                                                 23 days, found hvy cloud                                                  5    0.5 g urea; hvy. cloud                                                                       24 hrs.                                                                               0.058                                                                                83*                                                               23 days                                                                               0.02 94                                              6    0.25 g urea; opalescent                                                                      24 hrs.                                                                               0.13  62*                                                               17 days                                                                               0.17 50                                              7    0.10 g urea; opalescent                                                                      24 hrs.                                                                               0.21  38*                                                               17 days                                                                               0.26 52                                              8    0.05 g urea; opalescent                                                                      24 hrs.                                                                               0.27  21*                                                               17 days                                                                               0.29 15                                              __________________________________________________________________________      *PAINT KILL: good paint kill, dispersion and flocculation with PPG WHITE       and PPG high solids clear coat.                                          

EXAMPLES 9-12

In these examples, one starts with the same colloidal suspension as in Examples 1-8, but to the 50 melamine-formaldehyde dispersion one adds acetylacetone as specified in each example. The paint kill jar test was also carried out as in Examples 1-8.

Table II A shows the results of the jar test of Examples 1-8 but using the materials of Example 9-12. The results are reported as 9A-12A corresponding respectively to 9-12, Table II and Table II A.

                                      TABLE II                                     __________________________________________________________________________                      Time to                                                       Ex.              Develop                                                                              % H.sub.2 CO                                            No.                                                                               Treatment     Cloud Days                                                                               Found                                                                              Scavenged                                       __________________________________________________________________________      9 3.0 Acetylacetone; orange;                                                                   >110 days                                                                             3 hrs.                                                                            0.16                                                                               47                                                 sl. haze, phenol type odor                                                                          1  0.073                                                                              79                                                                      2  0.059                                                                              83                                              10 3.0 g Acetylacetone; orange;                                                                 >104 days                                                                             1  0.07                                                                               79                                                 sl. haze            21  0.05                                                                               85                                                                     51  0.05                                                                               85                                              11 2.0 g Acetylacetone; orange;                                                                 >104 days                                                                             1  0.1 71                                                 slight haze         21  0.09                                                                               74                                                                     51  0.11                                                                               68                                              12 1.0 g Acetylacetone; orange;                                                                 >104 days                                                                             1  0.18                                                                               47                                              __________________________________________________________________________

                  TABLE II A                                                       ______________________________________                                         PAINT KILL JAR TEST                                                            Ex                           Floc     Final Wtr                                No   Tack   Smear    % Float Description                                                                             Clarity                                  ______________________________________                                          9A  --     No       100     Excellent                                                                               Clear                                    10A  --     No       100     Excellent                                                                               Clear                                    11A  --     No       100     Excellent                                                                               Clear                                    12A  --     No       100     Excellent                                                                               Clear                                    ______________________________________                                    

EXAMPLES 13-20

In these examples, one starts with the same colloidal suspension as in Examples 1-8, but to the 50 g xelamine-formaldehyde dispersion one adds acetylacetone and urea as specified in each example. The paint kill jar test was also carried out as in Examples 1-8 where indicated. In Example 20, 550 g of the urea-formaldehyde dispersion was used. This would be equivalent to 0.38 g acetylacetone and 0.25 g urea had the same 50 gram aliquot been used. The purpose of Example 20 is to show that scaling up 11 fold still provides adequate formadehyde scavenging. As can be seen from Tables III, and III A, less urea and acetylacetone were used than when the individual components were used in Examples 1-8 and 9-12 respectively. Superior results are obtained. Table III A corresponds to Table III in the same manner as Table II A corresponds to Table II.

                                      TABLE III                                    __________________________________________________________________________                     Time to                                                        Ex.             Develop                                                                               % H.sub.2 CO                                            No.                                                                               Treatment    Cloud  Days  Found                                                                              Scavenged                                     __________________________________________________________________________     13 1.0 g Acetylacetone; stir;                                                                  >88 days                                                                              12    0.047                                                                              86                                               add 0.25 g urea     26    0.066                                                                              81                                                                   52    0.066                                                                              81                                            14 0.5 g Acetylacetone; stir;                                                                  add 24                                                                             hrs.                                                                              2     0.09                                                                               74                                               0.25 g urea         13    0.059                                                                              83                                                                   38    0.09                                                                               74                                            15 0.25 g Acetylacetone; stir;                                                                 >77 days                                                                              2     0.12                                                                               65                                               0.25 g urea         13    0.1 71                                                                   38    0.11                                                                               68                                            16 0.13 g Acetylacetone; stir;                                                                 >77 days                                                                              2     0.14                                                                               59                                               0.25 g urea         13    0.12                                                                               38                                                                   38    0.14                                                                               59                                            17 1.0 g Acetylacetone; stir;                                                                  5   days                                                          add 2.0 g urea                                                              18 0.75 g Acetylacetone; stir;                                                                 >32 days                                                                              7     0.05                                                                               74                                               0.25 g urea         14    0.04                                                                               78                                            19 0.38 g Acetylacetone; stir;                                                                 >32 days                                                                              7     0.06                                                                               68                                               0.25 g urea         14    0.05                                                                               74                                            20 4.18 g Acetylacetone; stir;                                                                 >11 days                                                                              10 min.                                                                              0.26                                                                               41                                               2.75 g urea         30 min.                                                                              0.23                                                                               43                                                                   50 min.                                                                              0.18                                                                               55                                                                   90 min.                                                                              0.19                                                                               53                                                                   150                                                                               min.                                                                              0.18                                                                               55                                                                   270                                                                               min.                                                                              0.16                                                                               60                                                                   420                                                                               min.                                                                              0.14                                                                               65                                                                   4  days                                                                              0.1 75                                            __________________________________________________________________________

                  TABLE III A                                                      ______________________________________                                         PAINT KILL JAR TEST                                                            Ex.                          Floc     Final Wtr                                No.  Tack   Smear    % Float Description                                                                             Clarity                                  ______________________________________                                         13A  --     No       95      Good     Clear                                    18A  No     No       90%     Light &  Clear                                                         10% sus-                                                                               frothy                                                                 pended                                                    19A  No     No       95%     Light &  Clear                                                         5% sus- frothy                                                                 pended                                                    ______________________________________                                    

EXAMPLE 21-31

In Examples 21-23 one again starts with the same colloidal suspensions as in Examples 1-8 but to the 50 g aliquot adds glyoxal as specified. As can been seen no formaldehyde was scavenged. However, when urea was first added stirred for one hour followed by glyoxal additions and again stirred for a quarter hour the amount of urea scavenged was greatly increased. The results are reported in Table IV below. In Table IV A the Paint Kill Jar Test was carried out, again showing the results wherein No. 24A corresponds to No. 24, etc. There is no Paint Kill Jar Test results for Examples 21-31 as glyoxal, per se, scavenged no formaldehyde.

                                      TABLE IV                                     __________________________________________________________________________                     Time to                                                        Ex.             Develop                                                                             % H.sub.2 CO                                              No. Treatment   Cloud                                                                               Days                                                                               Found                                                                               Scavenged                                        __________________________________________________________________________     21  1.2 ml glyoxal, 40% aq.                                                                    >59 days                                                                            5   0.24 0                                                                     17  0.24 0                                                22  0.6 ml glyoxal, 40% aq.                                                                    >59 days                                                                            5   0.24 0                                                                     17  0.24 0                                                23  0.3 ml glyoxal, 40% aq.                                                                    >59 days                                                                            5   0.21 0                                                24  0.2 g urea; stir 1 hr;                                                                     >62 days                                                                            7   0.031                                                                               91                                                   add 0.88 ml 40% glyoxal                                                                         23  0.02 |90                                     25  1.0 g urea; 0.88 ml 40%                                                                    >59 days                                                                            1   0.02 |90                                         glyoxal                                                                    26  0.5 g urea; 0.88 ml 40%                                                                    >59 days                                                                            1   0.38 80                                                   glyoxal                                                                    27  1.0 g urea; 0.44 ml 40%                                                                    >59 days                                                                            1   0.02 |90                                         glyoxal          21  0.02 |90                                     28  0.5 g urea; 0.44 ml 40%                                                                    >59 days                                                                            1   0.025                                                                               87                                                   glyoxal          21  0.02 |90                                     29  0.2 g urea, but 1.76 ml                                                                    >62 days                                                                            7   0.034                                                                               90                                                   40% aq. glyoxal  23  0.02 |90                                     30  1.0 g urea; 1.76 ml                                                                        >59 days                                                                            1   0.025                                                                               87                                                   40% glyoxal      21  0.02 |90                                     31  0.5 g urea; 1.76 ml                                                                        >59 days                                                                            1   0.064                                                                               66                                                   40% glyoxal      21  0.03 90                                               __________________________________________________________________________

                  TABLE IV A                                                       ______________________________________                                         PAINT KILL JAR TEST                                                            Ex.                          Floc     Final Wtr                                No.  Tack   Smear     % Float                                                                               Description                                                                             Clarity                                  ______________________________________                                         24A  No     Some      90     Light    Clear                                    25A  Yes    Yes       95     Tight pack;                                                                             Clear                                                                 light; frothy                                                                  Encapsulated                                                                   live paint                                        26A  Yes    Yes       97     Light; frothy                                                                           Clear                                          (live paint)                                                             27A  No     Lgt Smear 97     Tight pack;                                                                             Clear                                                                 light; frothy                                     28A  No     No        90     Light; frothy                                                                           Clear                                    29A  No     Some      85     Light    Clear                                    30A  No     Lgt Smear 85     Bubbles; no                                                                             Clear                                                                 floc                                              31A  No     Some      70     Very loose,                                                                             Clear                                                                 tiny floc                                         ______________________________________                                    

Although the definitions of the "paint kill jar test" are fully described in the Faust et al application, which was incorporated by reference, for the sake of completeness, the definitions are briefly described here. After adding the coagulant and stirring, a froth or "floc" appears on the top of the jar. This floc is coagulated particles of "detackified paint". "Tack" is the tackiness of the paint and is inversely proportional to the effectiness of the treatment, e.g. no tack means good killing of the paint. The "smear" is readily obtained by smearing the floc between ones thumb and forefinger. Other equivalent tests can be made. The "% float" is the percentage of the floating floculated material. The "final wtr clarity" is the clarity of the water beneath the floc.

Although specific melamine-formaldehyde dispersions are used in the specific examples, the formaldehyde scavenging properties of my invention are equally applicable to other formaldehyde resin detackifiers. A desirable formulation is a blend of about 98% melamine formaldehyde dispersion, about 1.5% acetylacetone and about 0.5% urea. The presently most preferred formulation is a blend of about 98.5% melamine-formaldehyde dispersions, of about 0.5% glyoxal 40% aqueous and about 1.0% urea; all percentages being by weight. 

What is claimed is:
 1. In a method of detackifying over-sprayed, water-insoluble paint in a spray booth operation, which comprises contacting over-sprayed, water-insoluble paint with paint spray booth water containing a melamine-formaldehyde polymer detackifier, the improvement comprising adding to said paint spray booth water a malamine-formaldehyde polymer detackifier containing a formaldehyde scavenging agent comprising urea and glyoxal in an amount sufficient to reduce the amount of free formaldehyde in the polymer to less than 0.15%.
 2. The method of claim 1, wherein a polymeric coagulant is also added to the paint spray booth water in an amount sufficient to flocculate detackifier paint.
 3. In a method of detackifying over-sprayed, water-insoluble paint in a spray booth operation, which comprises contacting over-sprayed, water-insoluble paint with paint spray booth water containing a malamine-formaldehyde polymer detackifier, the improvement comprising adding to said paint spray booth water a melamine-formaldehyde polymer detackifier containing a formaldehyde scavenging agent comprising urea and acetylacetone in an amount sufficient to reduce the amount of free formaldehyde in the polymer to less than 0.15%.
 4. The method of claim 3, wherein a polymeric coagulant is also added to the paint spray booth water in an amount sufficient to flocculate detackified paint. 